In photographic processing for photographic light-sensitive materials, it is desired to shorten the processing time and reduce the amount of waste solutions that are generated in processing.
A high-sensitivity negative type photographic light-sensitive material generally employs a silver iodobromide emulsion; however, in order to satisfy the above noted requirements, a silver chlorobromide emulsion or a silver chloride emulsion having a high solubility is useful. On the other hand, for reducing the amount of processing waste, it is desirable to increase the image density using a smaller amount of silver, and also it is well known in the art that tabular silver halide grains provide favorable properties with respect to sensitivity, graininess, sharpness, color sensitizing efficiency, etc.
Silver halide grains having a high silver chloride content, i.e., as high as 50 mol %, (hereinafter, "high silver chloride content grains") generally have a cubic structure. To form tabular grains having a high silver chloride content, various specific means must be employed.
Methods for preparing tabular silver chlorobromide grains are known including, for example, (1) simultaneously introducing an aqueous solution of a chloride and an aqueous solution of a silver salt in a dispersion medium in the presence of ammonia by a double jet method as described in JP-B-64-8324 (the term "JP-B" as used herein means an "examined Japanese patent publication"), (2) reacting an aqueous silver salt solution and an aqueous solution of a chloride-containing halide in the presence of aminoazaindene and a thioether bond-containing peptizer as described in JP-B-64-8326, (3) simultaneously introducing an aqueous solution of a silver salt, an aqueous solution of a chloride, and an aqueous solution of a bromide to a dispersion medium while keeping the mol ratio of chloride ion to bromide ion in the range of from 1.6:1 to 258:1, and keeping the total concentration of halogen ions in the range of from 0.10 to 0.90 normal as described in JP-A-58-111936 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), (4) introducing silver ion into a dispersion medium containing at least 0.5 molar chloride ion and a gelatin deflocculant formed from methionine of less than 30 .mu.mol per gram as described in JP-A-62-163046, (5) contacting a chloride-containing halide and a water-soluble silver salt in a dispersion medium in the presence of a crystal habit changing amount of aminoazapyridine and the salt thereof as described in JP-A-63-281149, (6) mixing an aqueous silver salt solution and an aqueous halide solution in the presence of thiourea or a thiourea derivative or using a gold compound as described in JP-A-63-213836, (7) forming the silver halide grains in the presence of a compound having a sulfur ion in a heterocyclic ring thereof as described in JP-A-63-2043, and (8) forming the silver halide grains in the presence of a carbonyl compound containing a sulfur ion in the molecule thereof or a sulfone compound as described in JP-A-63-41845.
However, a silver chlorobromide emulsion tends to fog and has a low light sensitivity as compared to a silver iodobromide emulsion. Also, the application of a silver chlorobromide emulsion is limited to color photo- graphic papers and light-sensitive materials for making printing plates using a relatively high intensity exposure.
For solving the above noted problems of high silver chloride content emulsions, various techniques have been proposed.
For example, JP-A-58-95736, JP-A-58-108533, JP-A-60-222844, and JP-A-60-222845 disclose that for imparting high sensitivity to a high silver chloride content emulsion, it is effective to form a grain structure having a high silver bromide content layer in the silver halide grains. The present inventors have found that although high sensitivity is obtained using these techniques, desensitization tends to occur when pressure is applied to the emulsion. Also, tabular silver halide grains having a uniform grain size distribution are difficult to prepare, such that the emulsion is not practically employed. Furthermore, it has also been found that by using these methods, it is difficult to sufficiently improve the reciprocity law failure of the high silver chloride content emulsion.
JP-A-51-139323, JP-A-59-171947 and British Patent 2,109,576A described that high sensitivity is obtained and the reciprocity law failure is improved by introducing to the silver halide emulsion a compound of a metal belonging to Group VIII of the Periodic Table.
Also, U.S. Pat. No. 4,269,927 describes that high sensitivity is obtained by incorporating cadmium, lead, zinc, or a mixture thereof in a surface latent image-type high silver chloride content emulsion having a silver chloride content of at least 80 mol %.
However, by using the above-described method, although a small increase in sensitivity and improvement in reciprocity law failure is observed, the resulting high silver chloride content emulsion does not provide practically useful performance.
Furthermore, European Patent 336426Al discloses a technique of obtaining high sensitivity by forming a high silver chloride content emulsion in the presence of six-coordinate complex of rhenium, ruthenium, or osmium having a cyan ligand.
However, the sensitivity attained is far inferior to that of a silver iodobromide emulsion which is generally used.